1. Field of the Invention
The present invention relates to a rotary grinder with an improved ram and screen. Rotary grinders of the present invention are, for example, used to grind plastic or wood to reduce the size of the material to a desired size. Material to be ground is placed inside a hopper and a ram is used to force the material toward the rotor having a plurality of cutters thereon. The ram does not have to ride in horizontal channels on the sides of the hopper so material does not interfere with or jam the ram. Further, a grooved screen may be employed wherein the screen has a plurality of V-shaped grooves therein in which the cutters travel. This permits the cutters to "clean" the screen so that ground material, for example, plastic, does not block the openings in the screen.
2. Discussion of the Prior Art
Rotary grinders with forced horizontal feed are known, such as, for example, the ReTech Model RG-52 Rotary Grinder, wherein the ram compartment lower portion of the hopper of the grinder contains a pair of horizontal channels or grooves on the opposed sides of the hopper. A ram, typically horizontally driven by a hydraulic piston system, has its top plate or deck slidably received in the two opposed grooves, which are lined with a plastic bearing material, to reduce friction and prevent metal to metal contact. If a heavy load is dropped on top the ram during its travel, the large bearing surface of the grooves stabilize against the impact. A disadvantage of these grooves is that they are exposed on the inside of the hopper compartment and, as a result, can be jammed with small material which is to be ground. This can cause wear or failure of the plastic guide rails and can jam the ram and prevent horizontal movement of the ram. The long channels can also affect the strength of the hopper, as the channels traverse along most of the horizontal length of both sides of the hopper.
This channel system provides little or no stabilization in the vertical plane and result in rollers being added to the back side of the ram to improve this stability. However, because of the manufacture, additional clearance is provided between the periphery of the ram and the ram compartment and, therefore, the necessity of an elaborate seal system to close the gap.
In grinders such as the ReTech Model RG-52 Rotary Grinder, an arced screen is spaced from the rotor containing a plurality of cutters attached thereto. One grinder may have a plurality of screens, each with a different size openings therethrough. A screen with desired size openings is selected and positioned after the rotor. Only material which has been ground down to a sufficient size to pass through the screen openings will exit the grinder onto a conveyor or container. Ground material which is too large to pass through the screen openings will be reground to a smaller size. When grinding certain plastic, it has been found that the plastic will not pass completely through the screen openings but, instead, hangs up in the openings and results in a blockage of the screen openings and requires shutting down of the grinder to clear the plastic material from the screen openings.
German patent reference no. 3,932,345 teaches a typical rotor and cutters. U.S. Pat. No. 4,844,363 teaches a non-horizontal moving hopper ram wherein the ram is guided by a pair of grooved tracks 49. U.S. Pat. Nos. 5,509,613 and 5,344,088 teach material grinders having a ram driven by a pair of pistons 24 from hydraulic cylinders 23. U.S. Pat. No. 5,645,234 teaches another grinder having a ram head 50.